1. Field of the Invention
The present invention relates to a multiple intake valve engine having two or more intake valves per cylinder.
2. Description of the Related Art
In the field of engine design, multiple intake valves are often employed to improve the shape, size, arrangement, and so forth of the various intake ports, and thereby enhance the intake efficiency, maximum intake quantity, swirl characteristics, and so on.
An example of multiple intake valve engine is disclosed in Japanese Patent Application Laid-Open Publication No. 6-288239 and shown in FIGS. 9 and 10 of the accompanying drawings. With this multiple intake valve engine, two intake ports 51 and 52 are formed generally in parallel for a respective cylinder, the one intake port 51 is a helical port which charges a spiral flow into the cylinder 53, and the other intake port 52 has a recess 54 at a location immediately before the outlet of the other intake port 52 such that the charge within the port is blown back in the opposite direction by this recess 54. The synergistic effect of these flows of intake air produces and augments a swirl S within the cylinder.
However, the following problems are encountered with the intake port 52. Because the intake flow collides with the recess 54, there is a drop in the flow rate of the charge, so intake efficiency suffers. Also, when the valve lift of the intake valve 55 is small as indicated by the solid lines in FIG. 10, the port outlet is blocked by the umbrella-like head 56 of the intake valve 55, so the charge is deflected by the valve head 56 and flows along a desired route, as indicated by the arrow fi. When the valve lift of the intake valve 55 increases as indicated by the imaginary line, however, the blockage by the valve head 56 is eliminated, and the charge flows straight out along the shortest route, as indicated by the arrow f2, which conversely has the effect of canceling out the swirl S. This tendency is more pronounced at high engine speeds, i.e., when the intake flow rate is higher and the inertia of the charge is stronger.
As a remedy for this, Japanese Patent Application Laid-Open Publication No. 10-37751 discloses a technique of intentionally reducing the intake valve lift when this swirl-weakening flow of air (charge) occurs. This system, however, is undesirable in that the performance originally had by the intake port outlet is not fully taken advantage of Specifically, there is a substantial decrease in outlet area, the maximum intake quantity is reduced, and so on. Thus, a powerful swirl could not always be obtained under all circumstances with a conventional intake port arrangement. It was also difficult to achieve an increase in swirl without sacrificing intake quantity.
An object of the present invention is to overcome the above described problems of the conventional arrangements.
According to one aspect of the present invention, there is provided a multiple intake valve engine including a first intake port with a first outlet, and a second intake port with a second outlet and being provided downstream of the first intake port with respect to a swirl generated in a respective cylinder of the engine. A near-outlet part of the first intake port, which is positioned immediately before the first outlet, is directed toward a cylinder inner wall in the upstream vicinity of the second intake port outlet with respect to the swirl such that the charge from the first intake port is directed to the above-mentioned cylinder inner wall. In other words, the charge from the first intake port is oriented to a dead space in the cylinder between the first and second intake port outlets.
The first intake port may extend in a generally xe2x80x9cLxe2x80x9d shape such that an intake air flowing in the first intake port is turned by between 90xc2x0 and 150xc2x0, when viewed in plan view, toward the cylinder inner wall upstream of the second intake port outlet when it leaves the first intake port outlet. This angle of between 90xc2x0 and 150xc2x0 may be primarily determined by the near-outlet part of the first intake port.
The first intake port may have an inlet section extending downstream from an inlet of the first intake port, and a middle section extending downstream from the inlet section to the near-outlet part, and the middle section may curve in a generally C-shape away from the second intake port and protrude with respect to the generally straight inlet section when viewed from the top. The C-shape of the middle section may be turned counterclockwise to a certain extent with respect to the first intake port axial direction so that it becomes close to xe2x80x9cUxe2x80x9d, and the turning bottom of this xe2x80x9cUxe2x80x9d approaches a cylinder center. The maximum offset length of the middle section with respect to the first intake port inlet section (or first intake port axial direction) may be at least 0.5 W but no more than 0.75 W, where W is the inlet width of the first intake port. The inner surface of the first intake port is preferably formed as a smooth surface over its entire length. The cross sectional shape of the near-outlet part of the first intake port may have an oval shape.
Preferably, the second intake port is a straight tangential port, and in the vicinity of the outlet thereof, the second intake port is constricted so as to have a passage deflected on the opposite side from the first intake port.
The height location of the first intake port inlet may be higher than the first intake port outlet. The middle section of the first intake port may curve downward. Preferably, the first intake port outlet is formed below a line passing through an uppermost point of the first intake port inlet and touching a lowermost corner point defined by the downwardly curved middle section. The height location of the first intake port inlet may be lower than or equal to the height location of the second intake port inlet.